The present disclosure relates to turbocharger systems having a turbine bypass valve for selectively causing exhaust gas from an internal combustion engine either to pass through the turbine of a turbocharger or to bypass the turbine under certain operating conditions. The disclosure relates in particular to a vacuum or pressure actuator for providing the motive force to move the turbine bypass valve between its open and closed positions.
Turbocharger systems for internal combustion engines sometimes have to employ multiple turbochargers arranged either in series or in parallel in order to achieve a high pressure-ratio or high flow capacity at certain operating conditions. At less-demanding operating conditions, however, such large capacity is not required, and therefore it is common to include some type of bypass valve arrangement for bypassing one of the turbochargers when large capacity is not needed. Typically such a multiple-turbocharger system will include a turbine bypass valve arranged for selectively causing exhaust gas to bypass the turbine of one of the turbochargers. The turbine bypass valve may comprise, for example, a swing valve or a butterfly valve. It is common to employ a vacuum actuator for moving the turbine bypass valve. A conventional vacuum actuator essentially comprises a piston or diaphragm arranged within a cylinder to define a chamber that can be subjected either to a vacuum or to ambient pressure for causing movement of the piston within the cylinder. A compression spring is arranged in the chamber for urging the piston in a first direction, for example, to open the turbine bypass valve. The piston is moved in an opposite second direction (for example, to close the turbine bypass valve) by increasing the vacuum in the chamber so that fluid pressure on the piston overcomes the spring force. Reducing the vacuum allows the spring force to overcome the fluid pressure force and move the piston toward the open position.
The present disclosure concerns improvements in such turbocharger systems, and particularly in the actuator that provides the motive force for moving the turbine bypass valve.